Over time, the mechanization of the processes in lumber mills has permitted an increase in the speed of the associated operations such as, but not limited to, sawing, edging, trimming, planning, stacking and bundling. However, as it is the case for every process including multiple operations, for the overall process to be effective, lumber need to flow smoothly between successive operations. If one of the operations is slower than the others, the entire production is slowed down accordingly. Nowadays, in many lumber mills, this bottleneck occurs at the stacking stage, the stacking of the boards being the most time consuming operation.
Stacking requires laying layers of boards or lumber on top of each other. The layers are formed of a fixed number of boards (normally having similar length and width). Layers can be spaced apart by sticks, which are placed perpendicularly to the boards and spaced apart horizontally. Sticks are usually placed either between each layers, as is most common for drying, or only at each N layers, where N is an integer smaller than the total number of layers in the stack, in order to increase the stability of the stack.
Conventional stacking apparatuses usually proceed by lifting a layer of boards formed on transfer chains and moving it forward over a forming stack, using mechanical arms or forks. Once the new board layer extends over the stack, the mechanical arms or forks are removed from under the board layer, in order to deposit the boards onto the stack. During this removal of the mechanical arms or forks, a stopper is usually provided in order to prevent the boards of the new layer from moving toward the transfer chains and keep them above the forming stack. Whenever sticks are needed, they are deposited on the top layer of the stack by a stick placing apparatus before the dropping of a new board layer.
Known stacking apparatuses can for example be found in U.S. Pat. Nos. 5,613,827 and 4,384,814, as well as Canadian patents CA2,559,649, CA1,009,673, CA976,996, CA976,995, CA896,361, CA824,503 and CA578,589.
Typical mechanisms generally require the displacement of the mechanical arms or forks in upward, forward, downward and backward directions, which arms often need to be displaced over distances of several meters. Consequently, the speed of the overall process of stacking the boards is limited to the maximum pace of the arms or forks. This pace can be improved by providing multiple sets of arms or forks operating in an alternating manner, but such a set up also increases the number of mechanical components involved, and the overall complexity, space, and cost of the apparatus. As mentioned above, the maximum pace that can be reached by such apparatuses usually cannot cope with the pace of the other operations on the lumber mills chain of operations, all of which resulting in a bottleneck at this stage. Moreover, this process is power consuming as the mechanism constantly has to fight inertia in the course of its movements.
Hence, in light of the aforementioned, there is a need for an improved board stacking apparatus which, by virtue of its design and components, would be able to overcome or at least minimize some of the above-discussed prior art concerns.